why ancient mariner kills the albatross?

He had no reason; it was a foolish and cruel thing to do. It was an impulsive act bu someone with no respect for nature.

ancient mariner kills the albatross because he thinks that the albatross has become a bad evil for them and the albatross is the only reason for their suffering.

the ancient mariner killed the albatross because he thought that the albatross nothing that is good sign, as it only eat the food that the sailors gave her and the old mariner saw that there was no land or island near there.